This invention relates to an elevator hoist apparatus and, more particularly, to a gearless traction-type elevator hoist apparatus in which an elevator car and a counter weight are driven through main ropes by an outer rotor motor.
FIG. 1 illustrates in a schematic sectional diagram an elevator system in which the conventional traction-type gearless elevator hoist apparatus with an outer rotor motor is employed. It is seen that the elevator system is installed in a building B defining a hoistway H and a penthouse P having a floor F. An elevator hoist apparatus is installed on the floor F of the penthouse P. The conventional hoist apparatus comprises a support structure having a pair of pedestals 1 extending upwardly from the floor F and an elongated support member 2 which may be a cylindrical shaft fixedly supported at its opposite ends by the pedestals 1. The support shaft 2 has securely mounted on its center portion a motor stator 3 including an iron core 3a and a coil 3b. A drum-shaped sheave 4 having a cylindrical wall 4a on which grooves 4d are formed and a pair of substantially annular disc-shaped plates 4b is rotatably mounted on the stationary support shaft 2 by bearings 4c. It is seen that the cylindrical wall 4a of the sheave 4 has on its inner surface a motor rotor 5 including a plurality of iron cores. Thus, the stator 3 on the support shaft 2 and the rotor 5 rotatably supported by the sheave 4 around the stator 3 constitute a three-phase induction motor which can be controlled by voltage regulation or frequency regulation. This motor is an outer rotor motor because the rotor is disposed outside of the stator to rotate around the stator.
Three main ropes 7 are placed within the grooves 4d and wound around the sheave 4. The ropes 7 have at the one end thereof an elevator car 8 and at the other end therof a counter weight 9. A brake mechanism 6 is mounted on the pedestals 1 so that it can apply a braking force on the drumshaped sheave 4.
With the elevator hoist apparatus as above described, the diameter of the sheave 4 is determined by the diameter of the rotor iron core 5 which depends on the electrical characteristics of the motor. Therefore, the load torque with respect to the motor become large, making the diameter of the sheave 4 unneccessarily large.
Also, since the loads of the elevator car 8 and the counter weight 9 applied on the sheave 4 must be supported by two disc-shaped side plates 4b, the side plates 4b as well as the cylindrical wall 4a of the sheave 4 must be made strong enough to support the load, resulting in a heavy rotating structure. Since the rotary portion is heavy, the support shaft 2 and the pedestals 1 therefor must also be strong and heavy. It is desirable to decrease the unneccessary weight of the hoist apparatus.
Further, when the load acting on the sheav 4 through the main ropes 7 changes, the dimension of the air gap between the stator 3 and the rotor 5 of the induction motor changes, so that the operation of the motor varies to such an extent that the comfortable ride in the elevator car is not realized.